1,721,051 research outputs found
My perpetual cycle: from student to researcher to teacher to student ...
No full textThis contribution stems from the personal experience of the author regarding how he became acquainted with embryology and how he finally entered the field of developmental biology. It reports his feelings as a student of the Histology and Embryology course as it was taught in the late 1970s, and his present efforts in teaching developmental biology to university students. In the Developmental Biology course at Pisa University today, students are taught the tissue, molecular and genetic mechanisms that regulate development of several model systems. Drosophila is introduced at the beginning, because of the great knowledge that it has brought to the unraveling of the molecular aspects of development and because it allows several basic concepts to be introduced, and vertebrate systems follow. Other topics include the classic experiments on amphibian systems, which are explained in the light of recent molecular advances, as well as the genetically more versatile vertebrate systems such as the mouse
Beginning at the end: A developmental biology course at the University of Pisa (Italy), which begins with Drosophila molecular genetics
No full textMolecular switches generating cell diversity in the Xenopus retina
No full textWe are interested in the molecular mechanisms regulating the early eye development and the following processes of cell commitment in the neural retina of the frog Xenopus laevis. We have studied several homeodomain transcription factors that are involved in identifying the initial eye field and in addressing retinal precursor cells (RPCs) toward specific neuronal fates. A complex series of regulatory events ensures that these key regulators are produced in the right time and space within the developing retina to generate the different types of neurons according to a precise and evolutionarily conserved time schedule.
In Xenopus, the closely related homeodomain proteins XOTX5b and XOTX2 respectively promote photoreceptor and bipolar cell fates, and, consistent with their expression pattern, have distinct roles in the developing retina. We have identified a small 8-10 aa divergent region, downstream of the homeodomain, that is crucial for the different and specific activities of XOTX2 and XOTX5b: exchange of this “specificity box” between the two proteins, switches the activity of XOTX5b into that of XOTX2 and viceversa. This box also appears relevant for modulating XOTX synergy and interactive abilities of the two XOTXs with NRL, another key regulator of retinal commitment.
Photoreceptors and bipolar cells are generated at different time schedules during retinal histogenesis. Interestingly, we found that the two Xotx mRNAs and the mRNA for Xvsx1, another homeobox gene promoting bipolar cell fate, are subject to a tight translational control that allows their respective proteins to be produced according to the different time of generation of photoreceptor and bipolar neurons. This control depends on interactions between their 3’UTRs and specific microRNAs. We have identified candidate microRNAs that are downregulated during retinogenesis to provide the switch for translation of XVSX1 and XOTX2 proteins, therefore allowing their proper timing of expression
Unusual features of the urodele genome: Do they have a role in evolution and development?
No full textUrodeles are amongst the organisms with the highest C-values. They provide a useful system for studies of genome organization at both the chromosomal and the molecular level. In this contribution we discuss the general features of 'excess' DNA in urodeles and emphasize that the urodele genome is in a state of plasticity. That fluidity is due to various molecular mechanisms which are involved in its continuous turnover. The implications of this fluid, 'excess DNA' for evolution and/or development are considered
Evoluzione tra didattica e ricerca: evo-devo, ovvero nuovi materiali per la conoscenza dei meccanismi evolutivi
Full text linkNel 2009 si è celebrato il bicentenario della nascita di Charles Darwin e il centocinquantenario della pubblicazione dell’ “Origine delle specie”, il testo fondamentale che ha cambiato, per sempre, il nostro modo di interpretare il mondo e la vita. In seguito è divenuto chiaro che “Niente in biologia ha senso, se non alla luce dell’evoluzione” (Dobzhansky). Tuttavia, la didattica sull’evoluzione biologica e sulle scienze naturali è in forte ritardo nel nostro paese e recenti interventi governativi ne hanno messo in dubbio la piena dignità e necessità di insegnamento. Eppure mai come adesso abbiamo la possibilità di investigare, attraverso la ricerca, e di divulgare, attraverso la didattica, quella che è l’origine comune del mondo vivente e la sua progressiva diversificazione in “infinite forme e bellissime”, anche in termini meccanicistici e molecolari. Oggi lo studio genetico-molecolare dello sviluppo ha portato infatti alla nascita di una nuova disciplina (l’Evo-Devo, da Evolution e Development) che ci consente, per così dire, di guardare in faccia l’evoluzione e di capire con quali intimi meccanismi molecolari si sia potuta creare, attraverso i processi dello sviluppo, quella variazione morfologica necessaria all’evoluzione di nuove forme ed adattamenti, su cui la selezione naturale fa presa. Nel corso della lezione, saranno illustrati i meccanismi genetico-molecolari per la costruzione degli organismi animali, e come le loro modificazioni siano alla base della diversità morfologica; ed esempi che spiegano, oggi, il piano costruttivo di animali estinti da lungo tempo, del quale è rimasta traccia scritta nel DNA di organismi attuali. Cercheremo di rispondere a domande del tipo: perchè i serpenti sono così diversi dalle lucertole, pur essendo loro parenti stretti, e perché hanno così tante vertebre? come si originano i diversi modelli di pigmentazione degli animali?
L’Evo-Devo ci mostra oggi che i meccanismi molecolari per la costruzione degli organismi animali sono largamente condivisi. Il loro studio ci aiuta a comprendere, senza averne sconcerto, il nostro posto nella natura
Identification and evolution of molecular domains involved in differentiating the cement gland-promoting activity of Otx proteins in Xenopus laevis.
Full text linkOtx genes are a class of vertebrate homeobox genes, homologous to the orthodenticle gene of Drosophila melanogaster, that play a crucial role in anterior embryo patterning and sensory organ formation. In the frog, Xenopus laevis, at least three members of this class have been isolated: otx1, otx2 and otx5 (crx); they are involved in regulating both shared and differential processes during frog development. In particular, while otx2 and otx5 are both capable to promote cement gland (CG) formation, otx1 is not. We performed a molecular dissection of Otx5 and Otx1 proteins to characterize the functional parts of the proteins that make them differently able to promote CG formation. We show that a CG promoting domain (CGPD) is localized at the Otx5 C-terminus, and is bipartite: CGPD1 (aa210-255) is the most effective domain, while CGPD2 (aa177-209) has a lower activity. A histidine stretch disrupts CGPD1 continuity in Otx1 determining its loss of CG promoting activity; this histidine-rich region acts as an actively CG repressing domain. Another Otx1 specific domain, a serine-rich stretch, may also be involved in repressing Otx1 potential to trigger CG formation, though at a much lower level. This is the first evidence that these domains, specific of the Otx1 orthology group, play a role during development in differentiating Otx1 action compared to other Otx family members. We discuss the potential implications of their appearance in light of the evolution of Otx functional activities
Translational control in cortical development
Full text linkDifferentiation of specific neuronal types in the nervous system is worked out through a complex series of gene regulation events. Within the mammalian neocortex, the appropriate expression of key transcription factors allocates neurons to different cortical layers according to an inside-out model and endows them with specific properties. Precise timing is required to ensure the proper sequential appearance of key transcription factors that dictate the identity of neurons within the different cortical layers. Recent evidence suggests that aspects of this time-controlled regulation of gene products rely on post-transcriptional control, and point at micro-RNAs (miRs) and RNA-binding proteins as important players in cortical development. Being able to simultaneously target many different mRNAs, these players may be involved in controlling the global expression of gene products in progenitors and post-mitotic cells, in a gene expression framework where parallel to transcriptional gene regulation, a further level of control is provided to refine and coordinate the appearance of the final protein products. miRs and RNA-binding proteins (RBPs), by delaying protein appearance, may play heterochronic effects that have recently been shown to be relevant for the full differentiation of cortical neurons and for their projection abilities. Such heterochronies may be the base for evolutionary novelties that have enriched the spectrum of cortical cell types within the mammalian clade
Evolution of highly repeated DNA within the genus Triturus (Amphibia Urodela)
No full textHighly repeated DNA is a main feature of urodele amphibian genomes. In Triturus this class of DNA consists of several sequence families differently arranged at both the molecular and the chromosomal level, showing varying degrees of conservation across species. Present data on highly repeated DNA in Triturus are here summarized and discussed with regard to the evolution and possible functional role of these sequences
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